The major goal of this project is to define the molecular mechanisms responsible for mediating the distinct patterns of gene expression in cerebellar neurons. The project is divided into two parts. The purpose of Part I is to distinguish between two general models of the generation of cellular diversity in the brain: (1) that patterns of gene expression depend on changes in cellular environment brought about by migrations from the germinal zones; or (2) the program of gene expression in each cell type is fixed early in development, before migration from germinal zones. The cerebellum is wonderfully suited to such an examination. Part II of this project approaches the molecular basis of gene regulation during cerebellar development, beginning with the gene encoding glutamic acid decarboxylase (GAD), which we have cloned and studied in the present grant period. Because GAD is responsible for the production of GABA, the most abundant inhibitory neurotransmitter in the brain, a detailed study of the regulation of the GAD gene will have intrinsic interest. The proposed studies of GAD regulation will also establish our ability to deal with the regulation of other genes during neural development. This project will have three specific aims: 1. To examine the appearance during normal cerebellar development of already identified mRNAs. These will include mRNAs encoding GAD, vitamin D dependent calcium binding protein, and cerebellin, all of which we have recently cloned. We will also study the mRNAs for GABA receptor polypeptides, which we and others are now attempting to clone, as well as for several other developmentally regulated polypeptides. 2. To examine the expression of individual genes in the cerebella of reeler, nervous, and staggerer mice. This will allow the evaluation of the influence of altered cellular environment on the expression of individual genes. 3. To identify cis regulatory sequences responsible for the cell type specific expression of the GAD gene and of genes whose expression responds to changes in cellular environment in the developing cerebellum.